Are all calories equal for weight loss? Not so say researchers

‘All calories are not created equal’ according to new research that suggests certain diets help to burn more energy than others.

The study challenges the notion that ‘a calorie is just a calorie’ from a metabolic point of view by suggesting that a low-glycemic load diet is more effective than conventional approaches at burning calories at a higher rate after weight loss.

"We've found that, contrary to nutritional dogma, all calories are not created equal,"​ said David Ludwig, director of the New Balance Foundation Obesity Prevention Center Boston Children's Hospital, USA – and a co-author of the study.

Writing in JAMA​, the team of US-based researchers examined the effects of three different diets – differing widely in macronutrient composition and glycemic load – on energy expenditure following weight loss.

Led by Dr Cara Ebbeling the scientists performed a controlled 3-way crossover trial involving 21 overweight and obese young adults – finding that resting energy expenditure and total energy expenditure were reduced more with a low-carbohydrate diet or low–glycemic index diet compared to a low-fat diet, despite all participants consuming the same amount of calories.

"Total calories burned plummeted by 300 calories on the low fat diet compared to the low carbohydrate diet, which would equal the number of calories typically burned in an hour of moderate-intensity physical activity,"​ she explained.

The researchers suggest that a strategy to reduce glycemic load rather than dietary fat may be advantageous for weight-loss maintenance and cardiovascular disease prevention.

“Ultimately, successful weight-loss maintenance will require behavioral and environmental interventions to facilitate long-term dietary adherence. But such interventions will be most effective if they promote a dietary pattern that ameliorates the adverse biological changes accompanying weight loss,"​ they conclude.

Commenting on the research via her Food Politics blog, Professor Marion Nestle of New York University, USA, noted that if the results of the new research are correct, people eating high-fat, low-carbohydrate diets are likely to have the easiest time maintaining weight loss.

“In contrast, people on low-fat, high-carbohydrate diets are likely to have a harder time maintaining weight loss,”​ she said.

The study ​

Each of the study's 21 adult participants (ages 18-40) first had to lose 10 to 15 percent of their body weight, and after weight stabilisation, completed all three of the following diets in random order, each for four weeks at a time.

The randomised crossover design allowed for rigorous observation of how each diet affected all participants, regardless of the order in which they were consumed:

A low-fat diet, which reduces dietary fat and emphasises whole grain products and a variety of fruits and vegetables – comprised of 60% of calories from carbohydrates, 20% from fat and 20% from protein.

A low-glycemic index diet made up of minimally processed grains, vegetables, healthy fats, legumes and fruits – with 40% of calories from carbohydrates, 40% from fat and 20% from protein.

A low-carbohydrate diet, modeled after the Atkins diet – comprised of 10% of daily calories from carbohydrates, 60% from fat and 30% from protein.

The team found that a low-glycemic index diet had similar metabolic benefits to a very low-carb diet – but without negative effects of stress and inflammation as seen by participants consuming the very low-carb diet.

They said that because they reduce the surge in blood sugar after a meal, both the low-glycemic index or the very-low carbohydrate–diet may be preferable to a low-fat diet for those trying to achieve lasting weight loss.

"In addition to the benefits noted in this study, we believe that low-glycemic-index diets are easier to stick to on a day-to-day basis, compared to low-carb and low-fat diets, which many people find limiting,"​ said Ebbeling.

"Unlike low-fat and low-very-carbohydrate diets, a low-glycemic-index diet doesn't eliminate entire classes of food, likely making it easier to follow and more sustainable."​